Computer systems configured as local area networks have been common for nearly two decades and are popular in a wide variety of business and educational applications. The most common LANs comprise a number of processing devices and a server that are coupled together by a hard-wired connection. Since about 1990, however, wireless local area networks (LANs) have become more common in the marketplace. Although the concept behind wireless LANS had been described a decade earlier, interest in LAN networks was limited until the release of the 2.4 GHz unlicensed band for industrial, scientific and medical (ISM) applications. Wireless LAN products most often employ either direct sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS) techniques to communicate between roaming mobile stations and network access points.
In a typical wireless computer network environment, the "backbone" of the LAN is a central server that communicates with a number of network access points through a hard-wired connection. Each access point (AP) includes a transceiver for communicating with at least one roaming mobile station (MS). The mobile station may be a point-of-sale terminal (i.e., an electronic cash register), a bar code reader or other scanner device, or a notepad, desktop or laptop computer. Each MS establishes a communication link with an AP by scanning the ISM band to find an available AP. Once a reliable link is established, the MS interacts with other mobile stations and/or the server. This allows the user of the MS to move freely in the office, factory, hospital or other facility where the wireless LAN is based, without being limited by the length of a hard-wired connection to the LAN.
Eventually, as a roaming mobile station moves in a multi-channel wireless LAN environment, the mobile station will move out of the range of its current access point. When this occurs, a "handover" takes place that breaks down the communication link between the mobile station and the current access point and establishes a new communication link between the mobile station and a new access point. The mobile station initiates this process when it detects that the link quality with the current access point has degraded below a specified threshold. The mobile station then begins looking for another access point, probably in a different frequency channel.
During this frequency scanning period, however, the mobile station will be tuned to a different frequency channel than is used by the current access point. Thus, any messages that are received by the current access point and destined for the mobile station that is scanning will be lost if transmitted during the scanning period. Present IEEE communication standards do not define protocols which allow the mobile station to inform the current access point that the mobile station is scanning and to request that the mobile station buffer any received messages for a short period of time.
Accordingly, there is needed in the art systems and methods that prevent loss of data during the scanning period of a roaming mobile station. There is a further need for systems and methods that prevent loss of data during the scanning period of a mobile station without modification of existing access points or wireless LAN systems.